Double Drift in DUNE: Discussion on HV Implications including - PowerPoint PPT Presentation

Double Drift in DUNE: Discussion on HV Implications including trade-offs between ACA and CAC configurations CERN, 20/6/2019 F. Pietropaolo

Double drift configurations for DUNE • Two possible configurations of the DUNE far detector with a doubled drift distance have been considered: - One central cathode plane and two APA array on the sides (ACA configuration) - Two cathode planes on the external sides and one APA array at the center (CAC configuration) • Both configurations require a partial redesign of some of the subsystems of the far detector. - The amount of modification needed in both cases are discussed in the document. - The most affected subsystems are the high voltage (HV) and photon detection system (PDS) and the cryostat/DSS design • It has been assumed that no modification will be done to the design of the APA and to Cold Electronics

DUNE SP Far Detector HV System 12m • Present TPC configuration: 3.5 m - APACACA: Chosen mainly to avoid HV facing too close to cryostat membrane • Double drift configurations: m 8 5 ~ APA CPA APA CPA APA CPA 7.0 m 3 4 June 2019 HVS-SP PDR Meeting

Common aspects to ACA and CAC • High Voltage on the CPA increased by factor of ~two, while maintaining the current CPA/Field cage concept (including ground planes): - Larger distance required from CPA outer edges to closest ground reference, to prevent discharges • Requirements for both configurations: - the absolute value of the electric field should be kept below the maximum acceptable value of 30 kV/cm - in any region of the cryostat; 
 - the energy stored between the field cage and the cryostat must be minimized as much as possible, to avoid damage to the cryostat and detector in case of fast discharges. • Doubling the distance from the CPA to the Top/Bottom Ground Planes from 30 cm to 60 cm is a reasonable approach to accomplish the above requirements. - CPA height need to be shortened by at least 60 cm (30 cm from upper and lower edges) with respect to the present configuration. • Inevitable redesign of CPA & field cage modules: - amount of redesign differs in the two configurations (ACA and CAC).

Proposed HV configurations

ACA configuration • Design more similar to current one (less R&D required): - Outer APA’s in the same position, CPA moved in the middle - Drift distance can be doubled (and include 1 APA thickness). - CPA plane structure and its construction / assembly operations can be maintained approximately as in the present design. - The field cage modules could rely on maintain the present design concept, however thicker I-beams would probably be required and the hanging/deploying operation should be revised due to the double length. - Ground planes as in present design - HV feed-through / cable and PS similar to NP02 • The requirement of unmodified APA structure and size implies: - "tilted" top/bottom field cage modules with a slight slope of ~30cm over 7 m drift length

HVS-SP design (evolution from TRD) Changes from the baseline design: Top ground plane installed as a separate but quick step to the DSS support Top ground plane directly supported by DSS beams. beams. No standoffs between FC and GP. EW profiles have bent corners to FC profile support I- close the large beams / box beams are gap in inside the field cage. No ProtoDUNE SP FC external insulators in high field region. 7 4 June 2019 HVS-SP PDR Meeting

Long FC modules • Typical FRP beams comes in 20’ length, some vendor seems to have 25’ length. • With hypothetical 7m long 6” FRP I-beam, the module has a deflection of about 4 cm warm, less than 2cm in LAr. 3.5 m 4” I-beam 6.4-7.0 m 6” I-beam

ACA configuration • Reduction of active volume: ~ 2.5%. - due to shorter CPA ad tilted FC modules - 1 APA volume gained • However: - Fiducial volume could be less affected due to reduced amount of passive material in LAr bulk • Interfaces with the cryostat and DSS structures; - displacement of the HV feedthrough ports - Two intermediate hanging beams removed. - Remaining beams in the same place as for the 3.5 m drift case; outer ones support APA; the central one for the CPA. - Current CPA DSS ports above the endwalls may be useful for the EWFC installation and support

CAC configuration • CPA layout modification : - the distance of the CPA from the long walls of the cryostat need to be increased with respect to the present 40 cm (distance of the APA to the cryostat walls in the 3.5 drift in current configuration). • mainly to avoid sparks from CPA to ground that could release the large energy stored in the CPA to membrane gap in the CAC configuration. - A detailed and careful study should be performed in order to address quantitatively this effect. - Further optimization of the cathode resistivity necessary to slow-down any potential discharges in order to minimise the instantaneous dissipated power. • Safe preliminary estimate: ~100 cm - similar to what is presently assumed in DUNE DP as cathode-to- cryostat distance. • As a consequence, the drift distance is reduced to at most 6.4 m.

CAC configuration • @ ~350 kV on CPA, energy stored in detector to membrane volume is ~ 1.5 kJ (3x ACA case) mainly at the CPA faces (with 1 m separation) • Electric field well below 30 kV/cm

CPA design: to be revised for CAC • Sharp edges of FFS • Surrounding profiles • Aluminum Hinges • the lifting bar under higher voltage

CAC configuration • Reduction of active volume: ~ 11 %. - due shorter drift distance (6.4 m) - In addition to shorter CPA and tilted FC modules • Interfaces with the cryostat and DSS structures; - major redesign of cryostat penetrations/rail suspensions due to • displacement of HV feedthrough ports • displacement the DSS outer beams to account for the 6.4 m drift distance (instead of 3.5+3.5m).

Construction/Assembly/Installation: CAC & ACA • The CPA assembly procedure will not chance with respect to the presently sequence: - Construction of base units (Panels+Frame+HVbus) at remote factories - Assembly in 11.4 m high columns in the clean room underground • Top and Bottom FC modules: - I-beams are industrially available up to ~ 6 m: being extruded bars, it should be possible to have them extended to 6.4 / 7 m (to be verified). - Sagging calculation could indicate that thicker beams are required: sagging itself is not an issue “electrically” provided that it is known. - Given the length of the beams, the modules should be preferentially assembled in the Clean room underground (but remote factory option not limited by size) • Deploying of T/B modules, End-walls: - It should be possible to adopt similar procedure to the one presently developed

Construction/Assembly/Installation: CAC & ACA CPA + Top FC installation/deploying • Similar installation sequence for CPA + Top FC as in the present design should be possible for both CAC and ACA • A manual 7+m gantry crane may be problematic for the Present Bottom FC installation (under evaluation) lower FC installation. • It should be possible to take advantage of the larger CPA- floor clearance to install the Bottom FC directly above the floor.

Risk and mitigation • Running at 320-350 kV on the CPA is an unexplored field. - ProtoDUNE NP02 would help clarifying how high this risk will be. - The design of the NP02 HV feedthrough require small modification to run at 350 kV. - Need some R&D for PS and cable (could be performed as intermediate step toward the 600 kV for DUNE-DP). • ProtoDUNE NP04 running stably at 180 kV. - If confirmed during the remaining of the long stability run, the minimal goal of 250 V/cm could be considered at reach. - this minimal goal acceptable only if the LAr purity in the far detector similar to that reached in ProtoDUNE NP04 - there is a tighter link between electric field and purity with a longer drift, similar to DUNE-DP • A higher risk is associated to the CAC configuration, since the surface area at maximum HV facing ground is larger. - Mitigation requires HV simulations and dedicated test (to be defined)

Impact on costs (rough estimate) • In the ACA configuration, overall CPA core cost is halved (only one CPA row instead of two): - potential core cost saving up to ~ 1.5 M$ • The total cost of the field cage modules should not vary considerably: the material budget is the same and the assembly operations could be very similar to present design. • Hanging and deploying procedures would deserve dedicated tests in Ash River. Higher costs would derive by the additional vertical ground planes, the higher resistivity Kapton layer, and the redesign of the cryostat facing CPAs for the CAC configuration. • The re-design and the related testing campaign of the two configurations described above imply a possible cost increase with respect to the present baseline layout. • A reliable estimate of these (probably non-negligible) costs requires a more in-depth revision of the HVS design.